When monarch butterflies wing their way south to central Mexico each fall, they use the sun to ensure that they stay on course. But how they head in the right direction on cloudy days has been a mystery.
It’s not unusual for animals engaged in long-distance migrations, including sea turtles and birds, to use an internal magnetic compass to get to where they’re going. But whether monarch butterflies have a similar ability had previously been unclear: Some studies had found weak evidence for a magnetic compass, while others found none at all.
It turns out the butterflies do use Earth’s magnetic field as a type of backup navigational system.
A paper published in the journal Nature Communications finally puts the issue to rest: The famous black-and-orange butterflies do, in fact, use a magnetic compass.
Researchers also found the reason for past conflicting evidence: The insects need ultraviolet [UV] light, which can penetrate cloud cover to power their magnetic compass—some of the previous studies didn’t provide the requisite illumination.
Butterflies may look fragile but evidence suggests otherwise:
- North American painted ladies lay their eggs in the deserts near the Mexican border.
- The orange butterflies, called painted ladies travel annually from the deserts of Southern California to the Pacific Northwest.
The butterfly, which is frequently mistaken for the monarch because of the similar colors, can move as fast a 25 mph and can go for days without stopping,
It can migrate up to 2,500 miles over mountains, seas and deserts and can travel at a much higher altitude than other insects.
- The painted lady is one of the most pervasive butterfly species in the world and is found on every continent except Antarctica and South America, according to National Geographic.
- Scientists estimate the migrating painted ladies number in the millions.